Variable Length at Age for Black Crappies and White Crappies in Missouri Small Impoundments

Abstract

I observed exceptionally variable TL at age for both Black Crappies Pomoxis nigromaculatus and White Crappies P. annularis in several small impoundments in northern Missouri. I used linear mixed models to assess the relative influences of sex, juvenile growth (back-calculated lengths at age 1 [L1] and age 2 [L2]), and age in explaining variation in TL of age-3 and older crappies. I also examined the potential effects of TL, age, and sex on body condition (relative weight W r) and TL, age, and W r on reproductive investment (gonadosomatic index [GSI]) of females. Models with various combinations of explanatory variables were compared with Akaike's information criterion. The most supported model explained over 60% of the variation in TL at age of age-3 and older fish and included age, L2, and sex for both species. For White Crappies, the L2-only model explained more variation in TL than the age-only model, but the opposite was true for Black Crappies. Logistic regression using TL and L2 as independent variables revealed that crappies of both species had less than a 50% probability of reaching 229 mm TL-a common minimum TL limit-by age 5 if L2 did not exceed 150 mm, indicating the importance of juvenile growth in determining adult size. The best model for W r included TL, age, and sex for both species but explained less than 19% of the variation in this variable. Likewise, the best models for GSI explained less than 10% of the variation and included TL and W r for Black Crappies and TL, W r , and age for White Crappies. Because of the importance of juvenile growth in determining sizes of adult crappies, future studies should focus on processes that influence growth rates during the juvenile phase.